Dynamic scalar and tensor polarizabilities of the 21Pand 23Pstates of He

The dynamic dipole polarizabilities at real and imaginary frequencies have been determined for the helium atom in its lowest singlet and triplet 2P states, using our time-dependent gauge-invariant method. Contributions of the 2S states to static polarizabilities are strong and negative, particularly in the case of the singlet 2 ${}_{}{}^1{}_{}{}^{}$P state, for which the static scalar polarizability ${\mathrm{\alpha }}_0$ is negative. The tensor polarizability ${\mathrm{\alpha }}_2$ corresponding to the differential Stark shift between the m Zeeman sublevels was also calculated and compared to previous theoretical and experimental results for the singlet 2 ${}_{}{}^1{}_{}{}^{}$P state. An evaluation of the ${\mathit{C}}_6$ dispersion coefficients for the 2 ${}_{}{}^1{}_{}{}^{}$P–2 ${}_{}{}^1{}_{}{}^{}$P and 2 ${}_{}{}^3{}_{}{}^{}$P–2 ${}_{}{}^3{}_{}{}^{}$P systems is also given, derived from the dynamic polarizabilities at imaginary pulsations ω.